Implement default init_custom_terrain() consistent with flat terrain …

…defintions in most prob.cpps

Source/prob_common.H

@@ -118,8 +118,26 @@ public:
                          amrex::MultiFab& z_phys_nd,
                          const amrex::Real& /*time*/)
     {
-        amrex::Print() << "Initialized flat terrain at z=0" << std::endl;
-        z_phys_nd.setVal(0.0);
+        amrex::Print() << "Initializing flat terrain at z=0" << std::endl;
+
+        // Number of ghost cells
+        int ngrow = z_phys_nd.nGrow();
+
+        // Bottom of domain
+        int k0 = 0;
+
+        for ( amrex::MFIter mfi(z_phys_nd, amrex::TilingIfNotGPU()); mfi.isValid(); ++mfi )
+        {
+            // Grown box with no z range
+            amrex::Box xybx = mfi.growntilebox(ngrow);
+            xybx.setRange(2,0);
+
+            amrex::Array4<amrex::Real> const& z_arr = z_phys_nd.array(mfi);
+
+            ParallelFor(xybx, [=] AMREX_GPU_DEVICE (int i, int j, int) {
+                z_arr(i,j,k0) = 0.0;
+            });
+        }
     }
 
 #ifdef ERF_USE_TERRAIN_VELOCITY